I'm on a Galaxy S6, Android 5.1.1.
I have already set up USB debugging for other applications, so Drivers and USB Debugging are active.

But when I type "opera:debug", I get "This Webpage is not available".
I tried it with latest "Opera Mobile 37.0.2192" and "Opera Mobile for Developers 41.0.2246".
Also tapping 'Installation-ID' seven times within Operas settings to enable developer mode didn't help.

Can anyone prove it is working?
Is there anything missing from the Guide referenced above?